According to FAO and WHO dietary fibres are constituents of substances of both animal and plant origin that are resistant to hydrolysis by human alimentary enzymes. Another generally accepted definition is that dietary fibres are the remnants of edible plant cell polysaccharides, lignin and other associated substances resistant to digestion by the alimentary enzymes of humans. According to these two definitions fibres can be obtained from grains, legumes, fruits, vegetables, algae or other plants or microbial or animal origin either as extracts, concentrates, bran or specific part of plant material containing a sufficient amount of active fibre ingredient.
The dietary fibres consist of insoluble and soluble substances. The insoluble polysaccharides include mainly cellulose and hemicellulose. The soluble polysaccharides include β-glucans, plant extrudates (gums), mucilages, legume seed gums, seaweed polysaccharides, bacterial polysaccharides, resistant starch or non-polysaccharide lignins. The cholesterol lowering effects have mainly been associated to soluble fibres because of their viscosity behaviour but also insoluble fibres may affect the serum cholesterol levels.
β-glucan and especially β-glucan from oat is known to have cholesterol lowering effect, which has been acknowledged also by health authorities. FDA has approved a health claim on the cholesterol lowering effect for oat products containing at least 0.75 grams of oat β-glucan per serving. The amount of β-glucan needed for an effect on cholesterol levels is 3 grams per day (recommended daily dosage) divided to 3 or 4 servings per day.
FDA has also approved a healthy claim for soluble fibre of psyllium containing at least 1.7 grams of soluble fibre per serving and the recommended daily intake of soluble fibre is 7 grams.
Consumption of diets with high β-glucan content has shown to lower the total and low density lipoprotein (LDL) cholesterol level by 8-12% (Ripsin et al., J. Am. Med. Assoc. 1992 (267) 3317-3325, Braaten et al., Eur. J. Clin. Nutr. 1994 (48) 465-474)
There is also evidence of the cholesterol lowering effect of the soluble fibres of psyllium (Anderson et al., Am. J. Clin. Nutr. 2000 (71) 1433-8) inulin (Causey et al., Nutrition Research 2000, 20(2), 191-201) and rye (Leinonen et al., J. Nutr. 2000 (130) 164-170) as well as microbial β-glucans (Bell et al., Crit. Rew. in Food Sci. and Nutr. 1999, 39(2) 189-202).
It is known that plant sterols (i.e. sterols and stanols) as well as esters thereof have serum cholesterol level lowering effects. Stanol fatty acid esters and the cholesterol lowering effects thereof are disclosed in U.S. Pat. Nos. 5,502,045 and 6,174,560 as well as a suitable method for their preparation.
Dietary intake of 2 to 3 g/day of plant sterols is reported to lower the serum LDL levels in man by on average 10%-14% thus reducing the risk of coronary heart disease (CHD). Plant sterols inhibit the absorption of biliary and dietary cholesterol from the intestinal lumen.
The current literature and especially FDA's conclusion to allow the health claim for plant sterols has increased the interest of the food industry in supplementing foods with plant sterols. Indeed, many such food items have recently been introduced into the market. It is assumed that new plant sterol containing foods will appear into the market rapidly.
This active launching of new plant sterol containing foods has raised a concern that a part of the population may have higher daily intake of plant sterols than needed to obtain an optimal cholesterol lowering effect. Short-term high intake of plant sterols has not been shown to be harmful. However, there are no data on possible long-term side effects of ingestion of high daily amounts of plant sterols. Furthermore, currently there is not a clear understanding on the biological impact of the increased serum level and thus higher systemic availability of plant sterols caused by increased intake from sterol-enriched foods, especially of foods enriched with unsaturated plant sterols (here called sterols). Therefore, there is a need of food products having a high enough reducing effect on total and/or LDL serum cholesterol levels and containing somewhat elevated levels of plant sterols, in which products the cholesterol reducing effect has still been enhanced by other means.